The Trophy Basement

From London to Los Angeles, some homeowners are burying their most opulent spaces underground. The rise of the subterranean mansion.

By

Candace Jackson

Updated March 16, 2012 10:43 a.m. ET

Wealthy home builders around the globe are digging deep.

In Los Angeles, builder Mauricio Oberfeld has buried about a third of his home underground: He built a contemporary 9,000-square-foot house for his family with a 3,000-square-foot basement. Glass stairwells lead to a lower level with an ornately tiled spa, large office, wine room and movie theater.

Photos: The Trophy Basement

In New York, Hamptons builder Joe Farrell's house has a 10,000-square-foot basement with amenities like a squash court and a two-lane bowling alley. Ron Papageorge Photography

From London to Los Angeles, some homeowners are burying their most opulent spaces underground. Candace Jackson on Lunch Break looks at the rise of the subterranean mansion. Photo: Noah Webb for The Wall Street Journal

"What you see from the street looks pretty low-key," Mr. Oberfeld says of the home, completed in 2010. "I don't like to be ostentatious and showing the world."

Formula 1 racing heiress Tamara Ecclestone is adding two underground stories totaling 5,000 square feet to her 17,000-square-foot home in London's Kensington neighborhood, purchased last year for $70 million. Features include a pool bar, billiard room, bowling alley and a nightclub, as well as a large gym and a game room for Ms. Ecclestone's boyfriend. Designer Gavin Brodin says the basement will also include a 3-D movie theater with eight custom-designed seats, each with its own built-in refrigerator and popcorn maker. Ms. Ecclestone, who declines to discuss the project's cost, says she wants the space for entertaining and adds that she decided to build downward because the home's historic status prohibited aboveground expansion.

"Everyone's digging these days," she says.

Some luxury-home builders are aiming to avoid the exterior footprint of a megamansion—without sacrificing the square footage or oversized amenities. Others are looking for a way around development restrictions that limit home sizes above ground. In many cases, the décor of these underground spaces rivals what's upstairs, with high ceilings, hand-painted mosaic tiles and limestone floors.

In central London's prime neighborhoods, high density, strict building codes and skyrocketing real-estate prices—up 43% since March 2009, according to real-estate firm Knight Frank—are resulting in some of the most elaborate subterranean living spaces in the world. Digging is under way to create one of the city's largest basements, doubling the size of Witanhurst House, a 45,000-square-foot home originally built in the 18th century. Plans approved by the district call for a two-story projection-screen movie theater; a large spa with a central rotunda; a 70-foot swimming pool with a two-story-high ceiling; bedrooms and staff quarters, according to public records. It's slated for completion this fall.

Architect Robert Adam, who is handling the home's expansion, declined to elaborate on the project, but says an underground pool does necessitate an additional story below for the water basin. "These things are very expensive to build," he says. The house was purchased by an unknown foreigner buyer through Safran Holdings, a British Virgin Islands-based company, for roughly $80 million in 2008. A representative for the company couldn't be reached for comment.

Southern California has become another hot spot for digging down. Rare until relatively recently, as land in the area is relatively plentiful, underground building activity grew in earnest after a 2008 Los Angeles ordinance limited the percentage of a lot a home could consume. "The relief valve to that was that if somebody put [square footage] underground and no one could see it," it was allowable, says Los Angeles city planner Erick Lopez. In most city neighborhoods, the aboveground square footage of newly built homes or expansions typically can't exceed 25% to 50% of the lot size, depending on neighborhood and topography. (Beverly Hills and other cities have a similar law on the books.)

As values for prime real estate begin to recover, the number of home-building permit applications that include a significant percentage of square footage underground has swelled. In London's Kensington and Chelsea neighborhoods, planning applications for subterranean development increased to 225 in 2011 from 179 in 2009, according to the borough. Alexander Lewis of Knight Frank says the phenomenon is growing in high-end neighborhoods because "people see it as a huge value to add to their property."

In Beverly Hills, construction workers are putting the finishing touches on a mansion owned by builder and architect Mohamed Hadid, who formerly designed, built and owned Ritz-Carlton hotels. Beneath roughly 30,000 square feet of house above ground is a basement of 14,000 square feet. Designed to be the entertainment centerpiece of the home, it has a ballroom that can seat 250, a Turkish-style bath with mosaic tiles and hand-carved Egyptian limestone columns, and a 50-seat movie theater.

"I like to call it the underground area," says Mr. Hadid. "Basement has an ugly connotation." He says the mansion will hit the market this spring for an estimated price of more than $60 million.

Republican presidential candidate Mitt Romney has filed an application to replace a single-story 3,000-square-foot beach house in La Jolla, Calif., with a 7,400-square-foot home with an additional 3,600 square feet of finished underground space, according to public records. A representative declined to comment. Tony Crisafi, one of the project's architects, declined to comment on Mr. Romney's motivations but says that these days, most of his clients want to be discreet about the scale of their home, and one way to do that is "by pushing things underground."

At least one planned house in Los Angeles's Brentwood neighborhood is putting the majority of its space in its two-level basement. According to public records, the city has approved plans for an 11,300-square-foot home that will have two levels underground measuring 30,000 square feet.

Joe Farrell, a Hamptons builder, says he's seen demand rise for trophy basements since he finished his 10,000-square-foot basement with a skateboard half pipe, spa, squash court and disco. The house is on the market for $43.5 million; he's rented it during prime summer periods for $550,000 for a two-week stay.

Elaborate basements in mansions have been popular in the past. Some Gilded Age mansions included basements with ballrooms and servants quarters. The Vanderbilt family's late 19th-century 175,000-square-foot Biltmore House in North Carolina has a below-grade level with a large kitchen, a swimming pool, gymnasium, bowling alley and servants' quarters.

Though technology has evolved to make more elaborate projects possible, building massive underground spaces can be difficult. "It's a formidable challenge to build under a building," says Rodney Gibble, a Manhattan-based structural engineer who says he's working on a growing number of basement expansions with swimming pools, gyms and small basketball courts. He says construction costs in New York below ground can be 50% to 100% more than the $800 to $1,000 per square foot cost of a high-end aboveground town house gut renovation.

In New York, soil types vary widely, as does bedrock. Usually, adjacent properties need to be underpinned, which is trickiest with soil. Breaking up bedrock and removing excavated matter by truck can be onerous in congested cities like New York and London. Hitting groundwater increases complexity and cost dramatically. If the water is contaminated, permits are needed to dispose of it.

Homeowners in the most expensive neighborhoods say the costs and headaches of digging are worth it. In London's most expensive districts, upper-end homes typically sell around $3,600 per square foot, basement square footages included. Darren Size, a London builder who recently doubled the size of a 10,000-square-foot home by building underground and is currently working on Ms. Ecclestone's home, says building very high-end finished basements typically ranges from $1,000 to $1,600 per square foot.

In Los Angeles and other parts of the U.S., digging underground can cost less than building above ground, particularly on sloped lots. But projects on geologically difficult sites often cost significantly more. Mr. Oberfeld, the Los Angeles builder, says his home was on a blue granite ridge. "To dig subterranean space here is a nightmare," he says. In other parts of the country, like South Florida, the topography and shallow waterline makes basements impossible.

Of course, in this price category it isn't enough to just build a basement—a common goal is to ensure it doesn't look like one. In Mr. Hadid's Beverly Hills house, what appears to be a skylight above the 36-foot Turkish bath is light refracted from hand-carved crystal panels. Some architects take advantage of a lot's slope, building in glass walls to light exterior rooms. In a few homes, builders have installed long tubes containing light amplifiers that run through the ceiling to channel daylight down. In homes where basements have been expanded beyond the house's footprint, skylights into gardens provide overhead natural light.

Builder Matt Dugally, Mr. Oberfeld's business partner, recently completed a home with a 5,000-square-foot basement in Orange County that has a golf-simulation center with putting and chipping greens, a driving range and a bar area modeled after the Tap Room bar at Pebble Beach. It's framed by wall-size high resolution photographs of the ocean. "Most basements we're doing now, they don't feel like basements," he says.

Interior designer Kelli Ford and her husband, banker Gerald J. Ford, built their Regency-style mansion with a large lower level in Dallas in 2008, partly so they could preserve the lawn on their six-acre property. The result is a 26,000-square-foot home with a 7,600-square-feet basement. The architect, Larry Boerder, extended the home's circular stairwell with a large first-floor window into the basement to bring natural light downstairs. The 5,000-bottle wine cellar is clad in basket-weave patterned limestone; chandeliers hang over a columned 20-by-50-foot pool.

Malibu-based architect Doug Burdge has designed basements for celebrity clients that display personal collections of dolls or antique clothing in faux "shops"; some of his parking garages double as party spaces. He recently built a 9,000-square-foot home for a family in Pacific Palisades with a 5,000-square-foot basement that has coffered wooden ceilings, a playroom and two bedrooms. His latest project: Prototype finished basements for a slate of speculative homes he's designing in the $10 million-to-$30 million range that will have private beauty salons and spas modeled after a line of Italian boutique hotels. The basements will contain big light wells, with sun falling onto bamboo tree courtyards.

The basement boom is already generating efforts to restrict it. In London, there have been complaints by neighbors unhappy about noise and vibrations from drilling and digging, which for large or complicated projects can last a year or more. In December, Malcolm Selsdon of the House of Lords introduced a "Subterranean Development Bill" to address concerns over damage to neighboring properties, soil erosion, loss of privacy during construction and financial concerns for homeowners who try to sell or rent their homes while a neighbor is digging. Lord Selsdon says the bill would limit the size and scale of such "iceberg developments," often with more volume underground than above.

Joseph Smith, an associate planner for the city of Malibu, says the city has taken steps to curb the trend. Older, more lenient basement rules that allowed for large, walkout basements—those which have a side that opens to the outdoors—were damaging the visual appeal of Malibu's hillsides, he says. A 2007 amendment did away with walkout basements and counted more underground space in a home's total allowable square footage.

Ms. Ecclestone, the Formula 1 heiress, model and television personality, says her home expansion is slated to be completed this fall. Along the way, Ms. Ecclestone has made a few changes to the plans, including nixing an initial layout that included a spa dedicated to her dogs. (The space will instead become an office.) The goal, she says, is to turn the basement into a space where she will entertain friends and family in private. "I feel like I'll never have to leave the house," she says.

The pool area alone in this basement is a sight to behold! When I searched for "finished basements," I did not expect to see something like this. I need ideas for my own basement that are a little bit more within my budget. However, it is always fun to see what other people can do with so much extra cash. http://www.ablehomerenovations.ca/en/services.html

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